From 3ff2f67a7c24183fcbcfe1332e5223ac6f96438c Mon Sep 17 00:00:00 2001 From: Evgeny Yakovlev Date: Mon, 18 Jul 2016 22:39:52 +0300 Subject: block: ignore flush requests when storage is clean Some guests (win2008 server for example) do a lot of unnecessary flushing when underlying media has not changed. This adds additional overhead on host when calling fsync/fdatasync. This change introduces a write generation scheme in BlockDriverState. Current write generation is checked against last flushed generation to avoid unnessesary flushes. The problem with excessive flushing was found by a performance test which does parallel directory tree creation (from 2 processes). Results improved from 0.424 loops/sec to 0.432 loops/sec. Each loop creates 10^3 directories with 10 files in each. This affected some blkdebug testcases that were expecting error logs from failure-injected flushes which are now skipped entirely (tests 026 071 089). This also affects the performance of block jobs and thus BLOCK_JOB_READY events for driver-mirror and active block-commit commands now arrives faster, before QMP send successfully returns to caller (tests 141 144). Signed-off-by: Evgeny Yakovlev Signed-off-by: Denis V. Lunev Reviewed-by: Paolo Bonzini Message-id: 1468870792-7411-5-git-send-email-den@openvz.org CC: Kevin Wolf CC: Max Reitz CC: Stefan Hajnoczi CC: Fam Zheng CC: John Snow Signed-off-by: John Snow --- include/block/block_int.h | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'include') diff --git a/include/block/block_int.h b/include/block/block_int.h index 8054146..a6b13ad 100644 --- a/include/block/block_int.h +++ b/include/block/block_int.h @@ -439,6 +439,11 @@ struct BlockDriverState { int copy_on_read; /* if nonzero, copy read backing sectors into image. note this is a reference count */ + CoQueue flush_queue; /* Serializing flush queue */ + unsigned int write_gen; /* Current data generation */ + unsigned int flush_started_gen; /* Generation for which flush has started */ + unsigned int flushed_gen; /* Flushed write generation */ + BlockDriver *drv; /* NULL means no media */ void *opaque; -- cgit v1.1